Field of the Invention
The present invention relates to a camera module, and more particularly, to a camera module including a voice coil motor actuator and auto focusing method thereof.
Discussion of the Related Art
Owing to the recent technical developments, multi-functional mobile terminals having various functions intensively integrated therein are released and mobile terminals tend to be downsized and lightened to fit the mobile environments despite functional complexity and diversity.
Therefore, a camera module installed in a mobile terminal such as a mobile phone, a laptop or the like tends to be downsized owing to the ultra-downsizing and ultra-precision of lenses.
An optical system of a camera module needs an auto-focus function to have a clear view of a target object that becomes a subject.
Such an auto-focus function uses actuators of various types in order to move a lens module to an optical focal position. And, performance of an auto-focus of a camera module can vary according to property of an actuator configured to transport a lens module.
Auto-focus actuators can include actuators of various types such as a voice coil motor (VCM) actuator, a piezo-electrically driven actuator, an MEMs actuator driven by static capacitance and the like.
With respect to a camera module that employs a voice coil motor actuator, permanent magnet is located at a fixing part of the camera module and a coil is attached to a lens module to be driven, whereby a magnetic circuit is configured. Hence, a lens module is driven by Lorenz Force that flows through the coil.
Thus, the camera module of the voice coil motor type extracts a difference of a magnetic flux value according to displacement of the lens module using a hole sensor, thereby calculating an optimal auto-focus value of the lens module.
However, such a camera module of a voice coil motor type should connect 4 power sources to a hole sensor, it has problem of a difficult manufacturing process.
Namely, in the camera module of the voice coil motor type, since at least 6 connectors including 2 connectors for electric connection to a coil located at the lens module and 4 connectors for electric connection to the hole sensor should be configured in the camera module, it is difficult to design such a camera module and the manufacturing process has many difficulties.
Moreover, with respect to the camera module of the voice coil type that uses the hole sensor, it takes a considerable time to move the lens module to an optimal position of auto focus and an auto-focus position error of the lens module may be generated due to hysteresis properties, structural friction properties and the like.